1. Field of the Invention
This invention relates to an improved insulated tubular and heat exchanger and a continuous fluid treatment apparatus such as may be used in down-hole wet oxidation of fluid waste streams, including municipal sludge.
2. Description of the Prior Art
Above ground wet oxidation systems have been in use for several years with limited success for the treatment of municipal sludge received from a sewage treatment process. The above-ground wet oxidation systems use high surface pressure and heat to initiate the wet oxidation reaction, however, the apparatus is not energy efficient, the system is subject to failure and results in only partial oxidation of the sludge; see for example, U.S. Pat. No. 2,665,249 of Zimmermann and U.S. Pat. No. 2,932,613 of Huesler, et al. The above ground wet oxidation processes have not therefore replaced the traditional methods of treating municipal sludge, which includes settling, dewatering, drying, incineration and the like.
Various vertical or down-hole fluid treatment systems have been proposed by the prior art but are used only in very limited applications. A down hole fluid treatment system utilizes vertical pipes which generally extend downwardly into the ground from a control station. The fluid to be treated is pumped into the vertical reactor pipes and the fluid head creates a pressure which assists in the desired fluid process or reaction. In the processes used to date, the reaction requires additional heat which may be added by electrical resistance coils or heated fluid which circulates in a heat exchanger. Air or other gases may be added to the fluid being treated to assist in the reaction.
Although several prior art patents propose a vertical well wet oxidation reaction system for treatment of municipal sludge or other fluid waste streams, the processes and apparatus disclosed in these patents have not been successful; see for example U.S. Pat. No. 3,449,247. As recognized by these prior art patents, the pressure created by the fluid head is dependent upon the length of the reactor. Thus, it is theoretically possible to fully oxidize municipal sludge at a depth of approximately one mile provided the concentration of the oxidizable material in the municipal sludge is balanced against the oxygen available in the air injected into the system. To the applicant's knowledge, however, no one has been successful in building a down-hole wet oxidation system for municipal sludge except the assignee of the present invention.
U.S. Pat. No. 4,272,383 of Dr. McGrew, entitled "Method and Apparatus for Effecting Subsurface, Controlled, Accelerated Chemical Reactions", assigned to the assignee of the present invention, discloses the principles of the first successful down-hole wet oxidation reaction system for municipal sludge which is now operating on an experimental basis in Longmont, Colo. The apparatus disclosed in the McGrew patent includes a series of generally concentric telescopically nested pipes or tubes wherein diluted municipal sludge is preferably received in the inner pipe and flows downwardly to a reaction zone adjacent the bottom of the pipe and recirculated upwardly through a second pipe, which surrounds the inner pipe, following the reaction. Compressed air is injected into the downwardly flowing sludge preferably in the form of Taylor-type gas bubbles. In the McGrew patent, the temperature of the reaction is controlled by a heat exchanger jacket which surrounds the inner concentric pipes wherein heated oil or other heat exchange fluid is pumped into the jacket to control the temperature of the reaction zone.
The fluid treatment apparatus of this invention preferably utilizes a centrally located heat exchanger wherein the fluid to be treated is contained within recirculating pipes which surround the heat exchanger, resulting in better control of the temperature of the reaction zone and more efficient heating of the fluid to be treated. The center downcomer pipe of the heat exchanger is preferably an insulated tubular which comprises two concentric pipes or tubes telescopically nested in spaced relation wherein the space between the tubes is sealed and preferably filled with an inert gas. As will be understood, the pipes and insulated tubular used in the fluid treatment apparatus of this invention comprises a series of pipes interconnected in a vertical string to accommodate the length of the overall fluid treatment apparatus. Insulated tubulars have been used in the oil well industry and other industries for several years to transfer heated fluids and gases. As set forth hereinbelow, however, the fluid treatment apparatus of this invention requires localizing the heat as much as possible in the reaction zone located adjacent the bottom of the pipes. The heated oil or other heat transfer fluid is received at the top of the apparatus or ground level. Thus, radial heat losses through the insulated tubular to the recirculated heat transfer fluid must be minimized. It has now been found that a substantial heat loss results from atomic hydrogen permeation into the space between the tubes of the insulated tubular which recombines to form gaseous hydrogen. There is therefore a need to develop an improved insulated tubular which inhibits hydrogen permeation to improve the insulation qualities of the insulated tubular which results in an improved heat exchanger and fluid treatment apparatus of the type disclosed herein.